Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $69.59   12.120%   $78.0243   $78.02   $78.00   $78.00  
  Purchase #2 $123.33   9.380%   $134.8984   $134.90   $134.90   $134.90  
  Purchase #3 $110.40   4.384%   $115.2399   $115.24   $115.25   $115.20  
  Purchase #4 $205.90   9.363%   $225.1784   $225.18   $225.20   $225.20  
  Purchase #5 $20.96   3.354%   $21.663   $21.66   $21.65   $21.70  
  Purchase #6 $224.45   4.504%   $234.5592   $234.56   $234.55   $234.60  
  Purchase #7 $247.46   7.744%   $266.6233   $266.62   $266.60   $266.60  
  7 purchase totals = $1,002.09       $1,076.1865   $1,076.18   $1,076.15   $1,076.20